Author Topic: Has anyone ever welded a piston, and used it?  (Read 2544 times)

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Offline John Orchard

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Has anyone ever welded a piston, and used it?
« on: October 31, 2022, 08:29:32 PM »
What are your thoughts on welding-up a couple of exhaust bridge lubricating holes in a piston? I imagine there wouldn't be enough heat to distort the piston?
Johnny O - Tahition_Red factory rider.

Offline sleepy

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Re: Has anyone ever welded a piston, and used it?
« Reply #1 on: November 01, 2022, 10:07:02 AM »
You would probably get away with it. More a problem of making the piston soft around the weld than distortion. A gentle pre-heat to about 150degC would be adviced before welding.
I many years ago welded holes in the top of pistons to get bikes going again for race meetings. I also welded up and re-machined broken ring lands in a V8 Chev Sprintcar piston as a desperate fix to race on the second night of a 2 night meeting and despite me warning them the piston stayed in use till the end of the race session.

Offline John Orchard

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Re: Has anyone ever welded a piston, and used it?
« Reply #2 on: November 01, 2022, 11:10:02 AM »
Thanks for input, I was also thinking of peening the hole closed with a centrepunch?
Johnny O - Tahition_Red factory rider.

Offline sleepy

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Re: Has anyone ever welded a piston, and used it?
« Reply #3 on: November 01, 2022, 12:40:09 PM »
Maybe if it was a forged piston but a cast piston could be a stress point.

Offline djr

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Re: Has anyone ever welded a piston, and used it?
« Reply #4 on: November 06, 2022, 08:09:57 AM »
Are they really small holes ?
If so I think your idea of peening them is probably the safest & easiest

Or block them with something like a piece of aluminium welding rod of a suitable size peened to hold in place

Or maybe cut a thread, then put a small aluminium bolt in, cut and carefully file down on the outside, peen or some other method to retain

All the above sound like lash ups, but would avoid any potential problems that may come from welding + if a small piece of aluminium did come out it would probably not damage anything on its journey out of the engine

good luck

Offline pokey

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Re: Has anyone ever welded a piston, and used it?
« Reply #5 on: November 06, 2022, 09:57:12 AM »
I would think the better solution would be the same as moving a ring locating pin. interference  fit of less than 1 thou and then finish by hand.

Offline John Orchard

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Re: Has anyone ever welded a piston, and used it?
« Reply #6 on: November 06, 2022, 11:23:54 AM »
I would think the better solution would be the same as moving a ring locating pin. interference  fit of less than 1 thou and then finish by hand.


Ah yes ! Good thinking.
Johnny O - Tahition_Red factory rider.

Offline James P

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Re: Has anyone ever welded a piston, and used it?
« Reply #7 on: January 20, 2023, 08:43:02 PM »
I know of someone who (in the 1980s) welded up the reed intake holes in DT175 pistons to use them in Lambretta piston-ported racing engines, so it can work. However, if it is only exhaust-bridge-lubricating holes you are dealing with, I wouldn't bother. I have been running a PE250 piston in a non-PE cylinder (with a single unbridged exhaust port) for more than 10,000km and the lubricating holes don't seem to cause any trouble.

Regards,
James

Offline John Orchard

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Re: Has anyone ever welded a piston, and used it?
« Reply #8 on: January 20, 2023, 10:28:14 PM »
I know of someone who (in the 1980s) welded up the reed intake holes in DT175 pistons to use them in Lambretta piston-ported racing engines, so it can work. However, if it is only exhaust-bridge-lubricating holes you are dealing with, I wouldn't bother. I have been running a PE250 piston in a non-PE cylinder (with a single unbridged exhaust port) for more than 10,000km and the lubricating holes don't seem to cause any trouble.

Regards,
James


Hmmm, thanks, interesting :-)
Johnny O - Tahition_Red factory rider.

Offline nifty

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Re: Has anyone ever welded a piston, and used it?
« Reply #9 on: March 01, 2023, 03:38:35 PM »
Might be off subject but I remember Nathan putting a hole in his piston at Glenbawn, installed a round head bolt and finished the meeting!

Offline Slakewell

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Re: Has anyone ever welded a piston, and used it?
« Reply #10 on: March 06, 2023, 05:45:23 PM »
One word Balance

Yes you can but will it vibrate like a room full of lesbians at wine night.
Current bikes. KTM MC 250 77 Husky CR 360 77, Husky 82 420 Auto Bitsa XR 200 project. Dont need a pickle just need to ride my motorcickle

Offline Momus

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Re: Has anyone ever welded a piston, and used it?
« Reply #11 on: April 18, 2023, 12:18:02 PM »
Whirly Wilson in Ararat puddle welded a 1975 DT400 piston that a Swedish traveller holed on the Western highway.

I was helping at the bike shop and took the piston down to Whirly's shed. He reckoned a bit of skirt from a Holden grey engine was the go and puddle cast the 10 mm or so hole with the oxy.

Owner rode off and all was good after the slight MJ blockage had been cleared.
If you love it, lube it.

Offline HL400

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Re: Has anyone ever welded a piston, and used it?
« Reply #12 on: April 21, 2023, 09:38:19 AM »
Hay John, there use to be a character in Bairnsdale that use to expand pistons !!!! he had 2 steal plates and would put he piston between them and fit a big G Clamp to hold them together then he would heat up the piston and screw the G clamp down then he would take it out and spin it in the lathe to fit the honed out bore,  IT SEAM TO WORK OK IN ag bikes

Offline sleepy

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Re: Has anyone ever welded a piston, and used it?
« Reply #13 on: April 21, 2023, 10:44:50 AM »
Piston expanding! That is changing the subject slightly. Many years ago as a broke teenager I had my TM125 piston expanded at the local engine reconditioning shop and it worked a treat for about 30 minutes then the piston exploded like a safety glass windscreen. Most of the piston ended up inside the low slung expansion chamber and it was just like the little cubes of the broken glass.
The machine that was used was a device that shot steel shot/balls into the inside of the piston which effectively expanded the piston. Only problem is it induced massive stress into the Japanese casting resulting in a rather short life. Luckily there was no damage to the bore, head or crank and after a clean out a new stock piston went back in with borrowed money from the old man.

Piston welding a burn hole isn't that bad a thing to do and I've done a few in the past to get bikes going again on a budget or in a hurry before a race meeting and as long as the reason for hole is fixed they seem to last. The original question here was about welding an exhaust bridge oil hole which has other problems like distortion and effecting heat treatment but the hole in the top doesn't cause any of those problems. I have recently doing some Bultaco cylinder boring and the pistons supplied had oil holes but no exhaust bridge to match. After a bit of research apparently Bultaco used to send out some new bikes that had the holes in them without the bridge and they didn't cause any running issues. The same pistons were in the Pursang models with an exhaust bridge but the Alpina of the same year didn't but still got the same piston or it could have been the other way around. Probably wouldn't see Jap bikes done like that but Bultaco probably just used what they had on hand and if it worked they just went with it.